This invention relates to the separation of methylolphenols from an organic solution. More particularly, the invention relates to the method of selectively separating methylolphenols from a solution containing the methylolphenols together with phenolic impurities.
Methylolphenols, also known as saligenins and hydroxybenzyl alcohols, have a number of commercial uses. For example, it has been known for many years that methylolphenols are intermediates in the production of phenolic resins. In recent years, methylolphenols have been disclosed to be useful as extractants for recovering boron values from boron-containing brines and for reducing the boron content of oil well brines, irrigation water and the like.
Methylolphenols may be prepared by a number of different methods such as, for example, the condensation reaction of a phenol with formaldehyde, the reduction of a salicylaldehyde by means of sodium amalgam, hydrogenation of salicylaldehydes over platinum black and the like. However, during the preparation of the methylolphenols, phenolic compounds other than the desired methylolphenols may also be formed and recovered with the desired product. In addition, methylolphenols are sensitive to heat and acid conditions with the result that the methylolphenols, when subjected to certain conditions during storage and/or use, tend to dimerize to form bis-phenols such as dibenzyl ethers and methylene dimers.
Generally, it is preferred to remove both the phenolic impurities formed during preparation of the methylolphenols and the bis-phenols which may form during storage or use of the methylolphenols, since their presence tends to adversely affect the properties and function of the methylolphenols. A number of techniques, such as selective leaching with organic solvents, chemical and adsorbent treatment and the like have been suggested heretofore for removing these phenolic impurities. However, these prior techniques are relatively complex, inefficient, or ineffective or they suffer from other disadvantages making their use less than completely satisfactory in a commercial operation.